What is the method for creating and using variables in SQL?

In SQL, you can create and use variables using the following methods:

1. Create a variable by using the DECLARE statement to define a variable, specify its data type, and assign an initial value. For example, DECLARE @myVariable INT = 10;
2. Assign a value to a variable: Use the SET statement to assign a value to a variable. For example: SET @myVariable = 20;
3. Using variables: In SQL queries, variables can be used in place of fixed numbers or strings. For example: SELECT * FROM table WHERE column = @myVariable;
4. The scope of variables: Variables can have a global scope or a local scope. Global variables are effective throughout the entire session, while local variables are only effective within the current program block or stored procedure.
5. Release variable: When a variable is no longer needed, you can use the DEALLOCATE statement to release it. For example: DEALLOCATE @myVariable;